Realization capable of allowing toner to undergo fixing at a lower temperature by lowering its softening point and glass transition point (Tg) relates to a decrease in the temperature during the fixing process, whereby it is possible to achieve significant energy saving of the electrophotographic process. Further, realization capable of achieving fixing at a lower temperature, namely at lower heat energy, makes it possible to match to a high rate process, resulting in beneficial productivity enhancement of copiers and printers. However, a mere decrease in thermal physical properties such as softening point or glass transition point of the toner degrades retaining properties and aggregation properties of the toner, whereby various adverse effects, such as developability degradation or localized clogging due to decrease in fluidity of the toner in the apparatus, occur. Even though retaining properties are improved via external additive techniques (such as the addition of fluidizing agents such as silica), drawbacks occur in which cleaning properties of the photoreceptor are degraded in a process employing a conventional electrophotographic photoreceptor, while employing a toner exhibiting lower thermal physical properties and an easily thermally deformable toner tends to adhere to the photoreceptor, so-called toner filming tends to occur, whereby use over a long period of time results in problems. Further, in full-color electrophotographic processes, which have increasingly been realized in recent years, image forming systems employing an intermediate transfer body are primarily employed. In such systems, a toner exhibiting lower thermal physical properties results in a decrease in the transfer ratio which is adversely affected by fusion onto the intermediate transfer body, whereby problems occur in which image defects such as center lower density or toner dots near characters tend to occur.
Known as a method to improve cleaning properties of residual toner on the electrophotographic photoreceptor and abrasion resistance of the electrophotographic photoreceptor is that endurance can be enhanced by increasing mechanical strength of the surface of a photoreceptor via incorporating hydrophobic silica into its uppermost layer (refer, for example, to Patent Documents 1-3). Further, it is known that by incorporating hydrophobic silica particles, prepared by treating the above hydrophobic silica with a silane coupling agent, into the uppermost layer of the photoreceptor, the mechanical strength of the photoreceptor is enhanced, and simultaneously, lubricants (metal carboxylates) are added, whereby photoreceptors exhibit higher endurance are prepared (refer, for example, to Patent Documents 4-6).
Further disclosed as a method to improve insufficient hydrophobicity of the above silica particles, which have been subjected to hydrophobic treatment, is a technique in which sintered silica is applied onto the surface layer of the photoreceptor (refer to Patent Document 7). Namely, described is a photoreceptor incorporating hydrophobic silica of an endothermic energy variation amount ΔH in the range of 40-200° C. of 0-20 J/g based on differential scanning calorimetry in the case of re-humidification under relative humidity of 80%, and a volume average particle diameter of 0.05-2 μm, and sintered silica is employed as hydrophobic silica particles employed in the aforesaid photoreceptor.
The above methods exhibit effects to improve cleaning properties of the residual toner on the electrophotographic photoreceptor as well as abrasion resistance of the electrophotographic photoreceptor. However, during image formation employing a low Tg toner, the resulting effects have been insufficient for the demanded higher level of the markets in which no image defects (such as center low density or toner dots near characters) occur.
(Patent Document 1) Japanese Patent Publication Open to Public Inspection (hereinafter referred to as JP-A) No. 56-117245
(Patent Document 2) JP-A No. 63-91666
(Patent Document 3) JP-A No. 1-205171
(Patent Document 4) JP-A No. 57-176057
(Patent Document 5) JP-A No. 61-117558
(Patent Document 6) JP-A No. 3-155558
(Patent Document 7) JP-A No. 8-202062